See: https://www.crowdsupply.com/oddly-specific-objects/sensor-wa... Answer: 1 to 2 years. My previous watch from the original blog post is still running on the original battery.
Coincidentally, your web site https://jgc.org/ is truly a lovely example of https://news.ycombinator.com/item?id=44613625 which was just discussed today as well.
Love your behind the screens stuff!
The airwolf one was funny, since it was a childhood favorite, and what a funny little typo they had there.
When watching the video I was thinking to myself, could this series have influenced my future interests in ways I didn't even know? Fun.